A rail-based transportation system such as a freight train typically comprises at least one locomotive and about one hundred rail-cars connected together by inter-car couplers. Most of the couplers that are currently used are connected to the rail-cars by a hydraulically damped spring. Since each of the couplers are connected to a hydraulically damped spring at opposite ends, there is a slack zone that allows the rail-cars to move relative to each other while in motion, allowing the train to change length by as much as 50-100 feet. For example, the slack zone will decrease to zero while the train is traveling downhill and using dynamic braking and will expand to its maximum length while the train is traveling uphill. The amount of movement allowed by the couplers depends on the handling of the locomotive controls. Typically, the couplers are subjected to two types of forces (i.e., static and dynamic) that may lead to breakage of the couplers, the brake pipe that prevents the rail-cars from banging in to each other, and the train. Accordingly, the train operator has to be careful in the handling of the locomotive controls so that these forces are not exceeded. In addition, the train operator has to control the locomotive so that the train travels within prescribed speed limits without excess acceleration and braking. Violation of the prescribed speed limits and excess acceleration and braking may lead to derailments and severe cargo damage. Therefore, it is imperative that the train operator handle the locomotive controls smoothly while staying within the prescribed speed limits.
Currently, most locomotives are equipped with only a very simplistic cruise control that uses a linear Proportional Integral (PI) controller. This type of cruise control can only be used below speeds of 10 mph and is primarily used for uniform loading and yard movement and cannot prescribe a braking action. In addition, this type of PI controller does not take into account the slack or distributed dynamics of the couplers in any manner and is not applicable for extended trains traveling at cruising speeds over a variety of terrain. Accordingly, there is a need for a speed controller that can smoothly manage the slack of the couplers while keeping the train within prescribed speed limits over a varying terrain.